1. Field of the Invention
The present invention relates to an apparatus and method for transmitting/receiving reference signal transmission information in a cellular radio communication system. More particularly, the present invention relates to an apparatus and method for transmitting/receiving reference signal transmission information in a Cooperative Multi-Point (CoMP) cellular radio communication system in which a plurality of Base Stations (BSs) provide a Mobile Station (MS) with a service using a CoMP scheme.
2. Description of the Related Art
Cellular radio communication systems have evolved to provide various high-speed large-capacity services to MSs. A typical example of the cellular radio communication system may include a High Speed Downlink Packet Access (HSDPA) mobile communication system, a High Speed Uplink Packet Access (HSUPA) mobile communication system, a Long-Term Evolution (LTE) mobile communication system, a Long-Term Evolution Advanced (LTE-A) mobile communication system, a High Rate Packet Data (HRPD) mobile communication system proposed in a 3rd Generation Project Partnership 2 (3GPP2), and an Institute of Electrical and Electronics Engineers (IEEE) 802.16m mobile communication system.
The LTE mobile communication system has been developed to effectively support a high-speed radio packet data transmission, and may maximize a throughput of a cellular radio communication system using various Radio Access (RA) schemes. The LTE-A mobile communication system enhances the LTE mobile communication system, and has an enhanced transmission capability compared with the LTE mobile communication system.
A 3rd Generation (3G) radio packet data communication system according to the related art, such as the HSDPA mobile communication system, the HSUPA mobile communication system and the HRPD mobile communication system, uses schemes such as an Adaptive Modulation and Coding (AMC) scheme and a channel adaptation scheduling scheme in order to enhance a transmission efficiency. When using the AMC scheme and the channel adaptation-scheduling scheme, a signal transmission apparatus may use an optimal modulation scheme and coding scheme in the most efficient timing point by receiving partial channel status feedback information from a signal reception apparatus.
In a radio packet data communication system using the AMC scheme, a signal transmission apparatus may adjust amount of data packets to be transmitted according to channel status. If the channel status is bad, the signal transmission apparatus may keep a reception error probability in a target reception error probability which the signal transmission apparatus targets by decreasing the amount of data packets to be transmitted. On the other hand, if the channel status is good, the signal transmission apparatus may keep the reception error probability in the target reception error probability and effectively transmit many data packets by increasing the amount of data packets to be transmitted.
In a radio packet data communication system using the channel adaptation-scheduling scheme, the signal transmission apparatus selects an MS having good channel status among a plurality of MSs, and provides the selected MS with a service. System throughput accordingly increases compared with a case that the signal transmission apparatus allocates a channel to an arbitrary MS, and provides the arbitrary MS with the service. Such system throughput increase is called as a ‘multi-user diversity gain’.
If the AMC scheme is used with a Multiple Input Multiple Output (MIMO) scheme, the AMC scheme may include a function for determining the number of spatial layers or a rank. In this case, the radio packet data communication system using the AMC scheme considers the number of layers to which packet data is transmitted using the MIMO scheme as well as a code rate and a modulation scheme in order to determine an optimal data rate.
Generally, if an Orthogonal Frequency Division Multiple Access (OFDMA) scheme is used, a system throughput increase is expected compared with a case in which a Code Division Multiple Access (CDMA) scheme is used.
The reason why the system throughput is increased if the OFDMA scheme is used is that a radio packet data communication system may perform a frequency domain-scheduling scheme. The radio packet data communication system may acquire more throughput gains upon using a characteristic of which channel status is varied according to a frequency like a case in which the radio packet data communication system acquires a throughput gain using the channel adaptation-scheduling scheme according to a characteristic of which channel status is varied according to time. Accordingly, in the next generation cellular radio communication system, techniques for changing the CDMA scheme used in a 2G cellular radio communication system and a 3G cellular radio communication system to the OFDMA scheme have been actively studied. The 3GPP and the 3GPP2 have started a standard project related to an enhanced cellular radio communication system using the OFDMA scheme.
FIG. 1 schematically illustrates a structure of a radio frame in an LTE-A mobile communication system according to the related art.
Referring to FIG. 1, 1 radio frame includes 10 sub-frames, and each of 10 sub-frames includes 2 slots. Indexes 0 to 9 are allocated to 10 sub-frames included in 1 radio frame, and indexes 0 to 19 are allocated to 20 slots included in 1 sub-frame.
FIG. 2 schematically illustrates a structure of a cellular radio communication system according to the related art.
Referring to FIG. 2, in a cellular radio communication system, a transmission/reception antenna is arranged at a center in each cell. In a cellular radio communication system including a plurality of cells, a particular User Equipment (UE) receives a radio communication service using a plurality of schemes as described above from a selected cell during a relatively long time, i.e., a semi-static time interval. For example, it will be assumed that the cellular radio communication system includes 3 cells, i.e., a cell 100, a cell 110 and a cell 120. The cell 100 provides a radio communication service to a UE 101 and a UE 102, the cell 110 provides a radio communication service to a UE 111, and the cell 120 provides a radio communication service to a UE 121. BSs 130, 131 and 132 manage the respective cells 100, 110 120.
The UE 102 receiving the radio communication service using the cell 100 is located at a point relatively distant from the BS 130 compared with the UE 101. The UE 102 suffers from a relatively large interference from the BS 132 managing a service region of the cell 120, so the UE 102 receives data at a relatively slow data rate.
If the cells 100, 110, and 120 independently provide a radio communication service, a BS managing a service region of each of the cells 100, 110, and 120 transmits a Reference Signal (RS) in order that a particular UE measures downlink channel status of each of the cells 100,110 and 120. If the cellular radio communication system is a 3GPP LTE-A mobile communication system, the RS is a Channel Status Information Reference Signal (CSI-RS).
FIG. 3 schematically illustrates location on which a CSI-RS is transmitted in a resource block in a LTE-A mobile communication system according to the related art. Each block in FIG. 3 indicates a Resource Element (RE) included in a resource block.
Referring to FIG. 3, in each of REs 200-219, CSI-RSs for distinguishing 2 CSI-RS antenna ports may be transmitted. A particular BS broadcasts 2 CSI-RSs for a downlink measurement through a RE 200. As described in FIG. 2, in a cellular radio communication system including a plurality of cells, each cell allocates a RE included in a resource block, and a CSI-RS is transmitted through the allocated RE. For example, in FIG. 2, a CSI-RS may be transmitted through the RE 200 in the cell 100, a CSI-RS may be transmitted through a RE 205 in the cell 110, and a CSI-RS may be transmitted through a RE 210 in the cell 120. As described above, in a LTE-A mobile communication system according to the related art, the reason why each cell transmits a CSI-RS using a different time resource and a different frequency resource is to prevent a mutual interference between CSI-RSs.
A sub-frame through a CSI-RS is transmitted may be determined using an ICSI-RS as a parameter transmitted through a Radio Resource Control (RRC) message. Upon receiving the ICSI-RS, a UE determines TCSI-RS as a sub-frame period of a sub-frame through which a CSI-RS is transmitted and ACSI-RS as an offset of the sub-frame through which the CSI-RS is transmitted using Table 1.
TABLE 1CSI-RSCSI-RS subframeperiodicity TCSI-RSoffset ΔCSI-RSCSI-RS-SubframeConfig ICSI-RS(subframes)(subframes)0-45ICSI-RS 5-1410ICSI-RS-515-3420ICSI-RS-1535-7440ICSI-RS-35 75-15480ICSI-RS-75
The UE receives a CSI-RS through a sub-frame satisfying a criteria expressed in Equation (1).(10nf+└ns/2┘−ΔCSI-RS)mod TCSI-RS=0  (1)
In Equation 1, nf denotes a Radio Frame Number (RFN), and ns denotes a slot number included in a radio frame. In an LTE-A mobile communication system, even though a particular sub-frame is determined as a sub-frame through which a CSI-RS is transmitted using Equation (1), the CSI-RS is not transmitted through the particular sub-frame in the following 3 cases:
1. a sub-frame through which at least one of a synchronization signal, a Physical Broadcast CHannel (PBCH) signal, and a System Information Block type 1 (SIB1) message is transmitted;
2. a sub-frame through which a paging message is transmitted; and
3. a sub-frame through which an SIB2 message to an SIB13 message are transmitted.
For example, the synchronization signal is transmitted through a sub-frame 0 and a sub-frame 5, the PBCH signal is transmitted through a sub-frame 0, and the SIB1 message is transmitted through a sub-frame 5 included in each of a radio frame satisfying a criteria of nf mod 8=0 to a radio frame satisfying a criteria of nf mod 2=0. The SIB1 message is transmitted by 80 [ms].
If the cellular radio communication system is a Frequency Division Duplexing (FDD) mobile communication system, a sub-frame through which a paging message is transmitted is set as one of a paging SFN set {9}, a paging SFN set {4, 9}, and a paging SFN set {0, 4, 5, 9} in a related radio frame by one of paging cycles 10 [ms], 20 [ms], 40 [ms], 80 [ms], 160 [ms] and 320 [ms]. A BS determines the paging cycle and the paging SFN set, and transmits the determined paging cycle and paging SFN set to UEs in a cell using a RRC message.
If the cellular radio communication system is a Time Division Duplexing (TDD) mobile communication system, a sub-frame through which a paging message is transmitted is determined using one of a paging SFN set {0}, a paging SFN set {0, 5}, and a paging SFN set {0, 1, 5, 6}. A BS determines one of the paging SFN set {0}, the paging SFN set {0, 5}, and the paging SFN set {0, 1, 5, 6}, and transmits the determined paging SFN set to UEs in a cell using an RRC message.
In the FDD and TDD mobile communication systems, an RRC message including information related to a sub-frame through which a paging message is transmitted includes a paging parameter including at least one of defaultPagingCycle information as paging cycle information and paging additional information (nB) included in an SIB2 message. The sub-frame through which the paging message is transmitted is determined using the defaultPagingCycle information and the nB in order to satisfy a criteria of Ns=max(1, nB/defaultPagingCycle). A relationship between the Ns and the paging cycle information is expressed in Table 2.
TABLE 2NsFDDTDD1{9}{0}2{4, 9}{0, 5}4{0, 4, 5, 9}{0, 1, 5, 6}
A sub-frame through which system information is transmitted is dynamically scheduled within a particular time window set as an SIB transmission period determined by a BS.
A size of a time window for transmitting the system information is determined based on a system information window length (si-WindowLength) parameter. An SIB transmission period for each of an SIB2 message to an SIB13 message for each SIB set is determined based on a system information period (si-Periodicity) parameter.
The si-WindowLength parameter and the si-Periodicity parameter as an upper layer signal are included in an SIB1 message, and the si-WindowLength parameter is commonly applied to all system information. The SIB set denotes a set of system information which is transmitted by the same period, and includes at least one of the SIB2 message to the SIB13 message. An example of an SIB type and an SIB period is expressed in Table 3.
TABLE 3SIB typeSIB periodSIB set 1SIB2, SIB3, SIB4 80 msSIB set 2SIB5, SIB6160 msSIB set 3SIB8320 ms
In an LTE-A mobile communication system where a transmission/reception antenna is arranged at the center of each cell, a UE may determine an SFN by detecting a synchronization signal and determine sub-frames through which a CSI-RS is transmitted and sub-frames, through which a CSI-RS is not transmitted, which collide with sub-frames through which a paging signal and system information are transmitted by receiving a PBCH signal and SIB messages.
In a cellular radio communication system in FIG. 2, there is a limitation for providing a high data rate to a UE located at a cell boundary due to interference from another cell. A data rate for a high speed-data service is strongly influenced by a location of a UE. In a cellular radio communication system according to the related art, it is possible that a relatively high data rate is provided to a UE located at a relatively close to a cell center; however, it is difficult to provide a high data rate to a UE located at relatively distant from a cell center.
In the LTE-A mobile communication system, a CoMP scheme in which a plurality of cells provide a communication service to a particular UE using a cooperation scheme has been proposed in order to provide a high data rate to a UE located at a cell boundary, and enlarge a service region providing the high data rate.
In the LTE-A mobile communication system, there is a need for distinguishing a sub-frame through which a CSI-RS is transmitted among sub-frames transmitted from a plurality of cells and a sub-frame through which a CSI-RS is not transmitted among the sub-frames in order that the UE effectively estimates channel status.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.